Along with the expansion and diversification of the optical fiber communications in recent years, various types of optical fibers adapted for respective uses have been developed and utilized. Various types of optical fibers, including a single mode optical fiber (hereinafter referred to as an SM fiber), a multi-mode optical fiber (hereinafter referred to as an MM fiber), a dispersion shifted optical fiber (hereinafter referred to as a DS fiber), and an erbium doped optical fiber (hereinafter referred to as an ED fiber), are provided. When these optical fibers are fusion spliced by a fusion splicing machine, it is required to make splicing under the fusion splicing conditions (discharge current, discharge time, etc.) suitable for each optical fiber. However, the type of the optical fiber may be mistaken, in which there is the risk that a splicing failure occurs due to unsuitable fusion splicing conditions for the optical fibers.
The fusion splicing of the optical fibers is not necessarily conducted under the light working environment, but may be conducted under the dark environment within a manhole, for example. In this case, the coating material of the optical fiber may be colored to identify the type of optical fiber, but recognized by mistake. If image observing means of high resolution and high magnification is employed for an image monitor of the fusion splicing machine, a core portion as minute as 3 to 10 μm can be observed, but the optical fibers of similar profiles may be recognized by mistake.
If the optical fibers are not spliced under the fusion splicing conditions suitable for the type of optical fiber, a splicing loss is greater, whereby the splicing of optical fibers must be made again from the beginning. To make splicing again, a series of operations, including the removal of a falsely spliced portion, the removal of the coatings for the end portion of optical fiber and cutting the end portion must be performed from the beginning, resulting in a worse working efficiency, and the operator becomes nervous.
One of the conventional techniques to solve the above problem is well-known in which the optical fibers are spliced under the optimal fusion splicing conditions by identifying the type of optical fiber through image processing, as disclosed in JP-A-8-21923. This conventional technique involves identifying the brightness level profile of the optical fiber observed at the fusion spliced portion through image processing. Then the brightness level profile (hereinafter referred to as a brightness profile) for each of various types of optical fiber is previously stored. Thereafter, the type of optical fiber is designated by collation with the brightness profile of optical fiber to be fusion spliced. The optical fibers are fusion spliced by designating the type of optical fiber and selecting the optimal fusion splicing conditions from among the stored fusion splicing conditions for each type of optical fiber.
However, when the type of optical fiber is estimated by obtaining the brightness profile from an observed image of the optical fiber, there are various intricate factors such that the brightness profile may be varied or different between the same type of optical fibers, depending on the focus or optical characteristics of the observed image, and the manufacturing conditions of the optical fiber. The conventional technique shows an example of a fusion splicing machine for ribbonized optical fiber, in which image observing means, typically with a low magnification and a long depth of focus, has a small numerical aperture of 0.1 or less. Hence, the resolution can not be sufficiently obtained, whereby it is difficult to acquire the detailed information from the brightness profile.
Even if image observing means with high magnification and high resolution is employed for image observation, a DS fiber and an ED fiber, for example, have both a core diameter of 4 μm, with quite similar brightness profiles, and practically is difficult to discriminate from the comparison between the brightness profiles. In the conventional technique, the comparison between the brightness profiles is made employing the interval between displaced points near the center of fiber axis. Accordingly, although this technique is effective when the brightness profile is clearly different depending on the type of optical fiber, it is difficult to discriminate all the types of optical fiber.
The present invention has been achieved in the light of the above-mentioned circumstance, and it is an object of the invention to provide an apparatus and method for fusion splicing the optical fibers under the fusion splicing conditions suitable for respective optical fibers in which the types of optical fibers can be fully discriminated.